Database Structure and Tables for SocialNetworking Website in SQL Server

Open SQL Server Management Studio 2008/2005 and Open a new Query Window.You can
also open new query window using shortcut key Clt+N
In the New Query Window create a database Named HeartBeatDB using the Following
Script

use master
create database HeartBeatDB
go

Database Tables SQL Script:

For this project we are creating three tables Register,Posts and Friends. Once the
Database is Created with the Name HeartBeatDB you can execute the below script to
create tables required for social networking website

After Executing this script three tables will be createda.Register Table- it will store all the information provided by the user during
registrationb.Posts Table - it will store all the posts written by the user on his wall or on
his friends wallc.Friends Table - it will store all the friendship status about the friend requests
send

if i develop another table called message, Do I want to set foreign key relationship? Here I didn't found any foreign key relationship. Without Foreign key relationship how it will work? explain please.